Quiet automatic volume control



IAug. 4, i936. s. w. SEELEY ET A1.

QUIET AUTOMATIC VOLUME CONTROL y2 sheets-sheet 1 Filed July 3.8, 1933www Eff INVENTORS Russ el/ M. P/anc/f arf W. See/ey /WI/u/l/ ATTORNEY-Fi i! )Immun ug. 4, 1936. s. w. SEELEY ET AL 2,049,750

QUIET .UTOMATC VOLUME CONTROL Filed July 18, 1933 2 Sheets-Sheet 2 1NENTORS Russe f M. P/cmc/r ATTORNEY- Patented Aug. 4, 1936 uiTED STATESOFFICE QUIET AUTOMATIC voLUME ooNTitoL Application July 1s, 1933, serialNo. 680,912

12 Claims.

This invention relates to receiving sets in Which automatic volumecontrols are employed with provisions to prevent the functioning of thesets until the carrier wave is properly tuned. Such receiving sets haveWhat is known as Q. A. V. C. operation. 'I'his term, as Will beapparent, is an abbreviation of the phrase quiet automatic volumecontrol.

An object of the invention is to produce Q. A. V. C. operation withminimum number of tubes.

Another object is to produce automatic volume control with a vacuumtube'tha't also constitutes the audio detector and amplifier.

Another object is to produce a negative bias on the control member of avacuum tube by a .diode rectifier contained in the same tube.

Another object is to produce a negative bias for automatic volumecontrol by rectified signal current in which the alternating `componenthas been filtered out.

Another object is to produce a negative bias on a control electrode of avacuum tube by rectified signal current with the alternating currentcornponent removed and reduce the positive bias on a rectifier cathodeby the` electron current controlled by said electrode.

Other objects willV appear in the following description, reference beinghad to the drawings in which:

Figure 1 is a schematic representation of the circuits employing theinvention.

Figure 2 is .a simplified illustration of vthe Q. A. V. C.y circuits.

Referring to the drawings:

I represents an antenna 'connected to ground 2 through coupling coil 3tuned to the signal by variable condenser 4. This antennacircuit alsoincludes blocking condenser 5 to prevent passage of the grid biascurrent to-the ground connection 2. The grid 6 of vacuum tube 1 isconnected to the tuned loop 3 Aand the cathode 8 of this tube isconnected through vbiasing resistance Y9 to the ground wire Ill.Condenser I4 is shunted around resistance 9 to bypass the radiofrequency component of the electron tube 1. Tube 1 has a screen grid I5connected by wire I6 to some intermediate positive potential at bindingpost I6. By Way of example this voltage Ymay be 671/2 volts. The plateI1 of this tube is connected through transformer coil I8 and wire `I9 tosomewhat higher positive potential at binding post 20, say volts. Thescreen grid I5 is connected toground wire I6 through radio frequencybypass condenser 2l.

The tuned loop 22 receives impulses from primary I8 and these areaugmented by resonance in the tuned loop and applied tothe grid 23 ofvacuum tube 24. The cathode 25 of this tube is connected through biasingresistance 26 to the ground wire Il). The screen grid 21 of this 5vacuum tube is connected to the wire I6 and the binding post I6'. 'Theplate 28 is connected through tuned loops 29 an-d 30 to the plate sourceconductor I9 and terminal 29. This conductor I9 is connected-to theground wire Il! through a l0- radiol frequency bypass condenser 3|. Theloop '30 is coupled for unicontrol with the tuned loops 3 and 22, asindicated. The'loop 39, however,'is arranged to tune either above orbelow in frequency, preferably above, the signal being re- 15 ceived soas to produce a super-audible intermediate frequency. The loop 29 istuned at the factory or at the service station to this intermediatefrequency. When this is once adjusted usually no further adjustments arerequired. The tuned 2o loop 39 is coupled to coil 32 shunted aroundresistance 26 but the shunted circuit has a blocking condenser 33 toprevent passage of direct current through this shunt. This loop 30 andthe shunt 32 constitute a feed-back arrangement 25 between `.the platecircuit and the grid circuit for producingV oscillations. The resistance26 contains direct current sinceit is in the electron circuit and thecontrol grid or electrode 23 of the oscillator-detector tube 24 isnegatively biased by 30 the Voltage across this resistance. This biasenables the oscillator tube 24 to detect the intermediate frequencycaused by the reaction of the signal with the oscillator frequency andit is this detected intermediate frequency that is fed 35 through loop29 and the tuned loop 34 connected to the grid 35 of vacuum tube 36. Thecathode 31 of this tube is connected through biasing resistance 38 totheground wire I0. Radio frequency bypass condenser 39 is shunted aroundthis re- 40 sistance. The screen grid 49 of the tube 36 is connectedthrough wire I6 to the positive terminal I6. The plate 4I of tube 36 isconnected to transformer coil 42 and tuning condenser 43 to the platesource conductor I9 and terminal 29.

The coil 42 is coupled to two secondary coils I3` 44. The tube 45 is atriode combined with a duplex diode for producing novel resultshereinafter to be particularly referred to. The diode plate 46V isconnected to coil 43 and the other end 50 of this coil is connectedthrough resistance `41 which is shunted by radio frequency bypass con-Vdenser 41') to ground wire I0 which is also connected to the negativeterminal 48 of thescreen grid, and plate voltage source. The seconddiode 55 'the resistance 41.

plate 49 is connected to coil 44 and the other end of this coil isconnected through resistance 59 to the cathode 5| of tube 45. An audiofrequency bypass or filter condenser 52 is shunted around thisresistance 59. The control grids or electrodes of tubes 1 and 36 areconnected through the automatic biasing conductor 53 through resistance54 to the negative terminal of This biasing conductor 53 is connected toan audio bypass condenser 55 for filtering out any audio component inthe biasing voltage. The plate 55 is connected through primary 51 to theplate voltage terminal 58 which may be a still higher positive terminal,say 180 volts. The control grid or electrode 59 is connected throughaudio coupling condenser v6| to an adjustable tap 62 on the resistance41. The point 6|] of this circuit is connected through resistances 63and 64 to the negative end of resistance 59 in the diode circuit. Audiofrequency filter condenser65 is connected between the cathode 5| and toa point between the two resistances 63, 64.

The cathode 5| of tube 45 is connected so that its electron currentpasses through resistance 65 to the negative terminal 61 which is thenegative end of a voltage supply, the positive end 68 of which isconnected to ground wire I5. The voltage between the terminal 61, 68,may be some intermediate Voltage such as volts. Resistance 66 is shuntedby'audio frequency bypass condenser 69. The cathode 5| `is alsoconnected through bypass condenser 10 to ground wire I0.

The primary of the coil 51 in the plate circuit of tube 45 may becoupled through any arrangement such as coil 1| to the output terminals12, 13, which may be connected to further audio amplifiers and aspeaker. Since these form no'part of the invention they are merelyindicated and not shown.

The cathode heaters of all the tubes are shown as being fed fromterminals 14, 15, of a direct current source.

The operation of the receiving system will now be described.

A clear understanding of the operation will be had by referring to thesimplified circuit of Fig. 2 insofar as the circuits are thereillustrated.

When no signal is being received there is no voltage induced in coils43, 44. Consequently no current flows in either circuit. The absence ofcurrent in coil 44 and resistance 50 leaves the grid 59 without anynegative bias. Consequently a sufficient current flows from terminal 58through coil 51, plate 56, cathode 5|, resistance 66 to negativeterminal 61 to bias the anode 45 negative to the cathode 5|. Hence nocurrent can ow in coil 43 until this cathode is reduced in potentialbelow the anode or plate 46.

In Fig. 1 when the signal comes in from antenna I through the radiofrequency amplifier 1 the oscillator-detector 24 and intermediatefrequency amplifier 36, intermediate frequency current commences to flowat once in coil 44 (Fig. 2) through resistance 59 to cathode 5| andthence to diode plate 49 as there is no bias'between the v anode andcathode in this circuit. The flow of current through resistance 50produces a negative bias through resistances 64 and 63 on the grid 59.This reduces the 'electron current flow- .ing through resistance 66below the no-signal ance 66, cathode 5| to plate 46. At this time thecombination of the Voltage drop in resistance 66 and the voltage betweenterminal 5'! and 68 makes the cathode 5| at thesame potential as orslightly negative to the anode 46. The signal current of the coil 43 isthus rectified. This rectified current has both a D. C. and an A. C.component. This D. C. component produces an automatic volume controlbias on the grids of tubes 1 and 36 through the resistance 54 andconductor 53. The audio frequency component is kept off of the grids byresistance 54 and condenser 55. The audio frequency component inresistance 41 is impressed directly on the grid 59 through adjustabletap 62 and audio` frequency coupling condenser 6|, that is, there is anaudio voltage drop across resistance 41. The tap 62 on this resistorbeing connected to grid 59, the other end returning to the cathode 5|through the voltage supply and condenser 59. The filter action ofresistor 64 and condenser 65 servesrto keep audio voltages which aredeveloped across resistor 50, due to rectifying action of diode plate49, from reaching the grid 59. The audio voltage is then amplifiedthrough variation of the plate circuit electron current and ampliedimpulses appear in the primary 51 and secondary 1| whence they may befurther amplified and reproduced in the loudspeaker not shown.

It takes apredetermined current in rectifier coil. 44 to reduce thepotential of lthe rectifier cathode 5 down to the potential of the anode46, so that no sound is produced in the speaker (not shown) until thesignal reaches the threshold value.

If the signal tends to increase, a greater bias will be produced inresistance 41 and a greater negative bias on the grids of amplifyingtubes 1 and 36 which will decrease the signal down to the desired level.The volume can be set to the desired value by adjusting the slidecontact 62 on the resistance 41 and when this is once set to the desiredvolume such volume will be maintained by the automatic featuresdescribed. Since no current can be rectified thru diode plate 46 until apredetermined threshold current is produced due to the negative bias ofthe anode 46, side band noises, hisses and other stray effects areeliminated. No signal effects can be produced on the grid 59 until thecathode 5| is reduced in potential below the anode 46 and this can onlybe produced by some sufficiently strong voltage such as will be producedby a signal wave. The arrangement therefore produces what is known as Q.AQV. C. operation where nothing is heard between the Various stationstuned in, the signal being only reproduced when the set is accurately intune with the carrier wave.

It will be apparent that we may secure many features of the improvementwithout using the combined diode-triode tube, as separate diodes orother rectifiers may be used exactly as indicated in Fig. 2.

It will also be apparent that we may modify the arrangement so Vas toproduce other features of the invention without combining them in such away as to produce all of them together. In other words, we may modifythe arrangement so as to produce any one of the desired featuresalone,.though, of course we prefer to produce all of them in combinationfor best operation of the receiving set.

Having described our claim is: 1 In radio receiving sets, an amplifyingtube,

invention, what we a rectier connected to'receive energy jfrom saidtube, asecond'amplier ltube connected to receive energy from saidrectier means including a second'rectifier to negatively Abiasrthe'anodeof said rectifier by space current in the second ampliiier, and means toreduce said bias to zero in response to current passing through the rstmentioned amplifier above a predetermined Value. Y

2. In radio receiving sets, an amplifying tube,

a rectifier vconnected to receive energy from said tube, a secondamplier tube connected to receive energy from said rectifier means tonegatively bias vthe anode of said rectifier by space current in theVsecond amplier, and means to reduce said bias Ato zero in response tocurrent passing through the rst Amentioned amplifier above apredetermined value, a resistance in circuit with said rectier, andmeans to apply a negative bias to the control electrode of the firstmentioned tube proportional to the current flowing through saidresistance.

Y3. In radio receiving sets, an amplifier tube, a rectiiier connected toreceive energy from said tube, a second amplifying tube connected toreceive energy from said rectifier, a resistance in the circuit of saidrectier, a resistance in the output circuit of the second amplier tube,means to negatively bias the anode of said rectier from the potentialdrop in the second resistance, and means to negatively bias the controlelectrode of the irst amplifying tube by the potential drop in the firstresistance.

4. In radio receiving sets, an amplier tube, a rectifier connected toreceive energy from said tube, a second amplifying tube connected toreceive energy from said rectifier, a resistancev in the circuit of saidrectifier, a resistance in the output of the second amplifier tube,means to negatively bias the anode of said rectifier from the potentialdrop in the second resistance, and means to negatively bias the controlelectrode of the iirst amplifying tube by the potential drop in thefirst resistance, a second rectifier connected to receive signal currentfrom the first amplifier, a resistance in circuit with the secondrectifier, and means to negatively bias the control electrode of thesecond amplifier tube by the potential drop in the third resistance.

5. In radio receiving sets, a resistance, a vacuum tube, a source ofsupply having high and intermediate positive voltage terminals and acommon negative voltage terminal, the highV positive voltage beingconnected to the anode of said tube and the negative voltage terminal toone end of said resistance, the other end of said resistance beingconnected to the cathode of said tube, a second resistance, a rectifierhaving its cathode connected to one end of said second resistance and tothe cathode of said tube and its anode to the other end of said secondresistance, a connection between said other end of the second resistanceand the control electrode of said vacuum tube, a second rectiiier havingits cathode connected to the cathode of said vacuum tube, a thirdresistance connected between the anode of the second rectier and theintermediate positive voltage terminal.

6. In radio receiving sets, a resistance, a vacuum tube, a source ofsupply having high and intermediate positiveA voltage terminals and acommon negative voltage terminal, the high positive voltage terminalsbeing connected to the anode of said tube and the Y negative voltageterminal to one end of said resistance, the other end of said resistancebeing connected to `the cathode of said tube, a rectifier having itscathode connected to one end of a second resistance and to the cathodeof said tube and its anode lto the other end of said second resistance,a

connection between said other end of the second resistance `and thecontrol electrode of said vacuum tube,V a second rectifier having itscathode connected to the cathode of said vacuum tube, a third resistanceconnected between the anode ofthe second rectiiier and the intermediatepositive voltage terminal of the second source, and a connection betweenthel control electrode of said tube and a point on the third resistance.Y

7. In radio receiving sets, a resistance, a vacuum'tube, a source ofsupply having high and intermediate positive voltage terminals andcommon negative voltage terminals, the high positive voltage terminalbeing connected to the anode of said tube and the negativ-e voltageterminal'to one end of. said resistance, the other end of saidresistance being connected to the cathode of said tube, a secondresistance, a rectier having its cathode connected to one end of saidsecond resistance and to the cathode oisaid tube and its anode to theother end of said second resistance, a connection between said other endof the second resistance and the control electrode of said vacuum tube,a second rectier having its cathode connected to the cathode of saidvacuum tube, a third resistance connected between the anode of thesecond rectiiier and the intermediate positive voltage terminal, avacuum tube amplier, means to connect the output of said vacuum tubeamplifier to both of said rectiers and a connection between the controlelectrode of said vacuum tube amplifier and the negative .end of thethird mentioned resistance.

8. In radio receiving sets, a resistance, a vacuum tube, a sourceofsup-ply having high and intermediate positive voltage terminals andcommon negative voltage terminals, the high positive voltage terminalbeing connected to the anode of said tub-e and the negative voltageterminal to one end of said resistance, the other end of said resistancebeing connected to the cathode of said tube, a second resistance, arectifier having its cathode connected to one end of said secondresistance and to the cathode of said tube and its anode to the otherend of said second I resistance, a connection between said other end ofthe seco-nd resistance and the control electrode of said vacuum tube, asecond rectiiier having its cathode connected to the cathode of saidvacuum tube, a third resistance connected between the anode of. thesecond rectifier and the intermediate positive voltage terminal, and a.connection between the control electrode of said tube and a point in thethird resistance, a vacuum tube amplifier, means to connect the outputof said vacuum tube amplifier to both of said rectiiers and a connectionbetween the contro-l electrode of said vacuum tube amplier and thenegative end of the third resistance.

9. In systems for detecting and amplifying signals above a predeterminedthreshold value, a rectifier for detecting said signals having an anodeand a cathode, an amplifier tube having its grid connected to received-etected signals from said rectifier, a direct current supply for theanode-cathode circuit of said ampliier tube, means to negatively biasthe anode of. said rectifier by a direct current potential in saidanodecathode circuit and a second rectier adapted to negatively bias thegrid of the amplifier tube with the direct current potential of therectified signal. v

10. In systems for detecting and amplifying signals above apredetermined threshold value, a radio frequency amplifying tube foramplifying said signals, a rectifier for detecting the signals ampliedby said tube and having an anode and cathode, an amplifier tube havingits grid connected to receive detected signals from said detector, adirect current supply for the anodecathode circuit of the secondmentioned amplifier tube, means to negatively bias the anode of saidrectifier by a direct current potential in said anode-cathode circuitand a second rectifier connected to the output of said radio frequencyamplifying tube and adapted to negatively bias the grid of the secondmentioned amplifier tube with the direct current potential of therectied signal and means to bias the grid of the radio frequencyamplifying tube by the direct current potential of the signal detectedby the first mentioned rectifier.

11. In systems for detecting and amplifying signals above apredetermined threshold value, a rectifier for detecting said signalshaving an anode and a cathode, an amplifier tube having its gridconnected to receive signals from said detector, a second rectifier forrectifying said signals, a resistance in circuit With said'rectierhaving its negative and positive ends connected respectively to the gridand cathode of said amplifying tube and a condenser adapted tosubstantially short-circuit the alternating current potential of saidresistance.

12. In systems for detecting and amplifying signals above apredetermined threshold value, a rectifier for detecting said signalshaving an' anode and a cathode, an amplifier tube having its gridconnected to receive signals from said detector, a second rectifier forrectifying said signals, a resistance in circuit with said rectifierhaving its negative and positive ends connected respectively to the gridand cathode of said amplifying tube, an impedance to alternating currentconnected between the negative end of said resistance and the grid ofsaid tube, and a low impedance condenser in shunt to the firstresistance.

STUART W. SEELEY. RUSSELL M. PLANCK.

